The construction industry is one of the largest carbon emitters worldwide. Understanding the carbon footprint of building materials is important for reducing environmental impacts from the design and construction process.
The industry has made strides in operational energy consumption through efficiencies and renewable energy options, but embodied carbon is a more elusive target.
Concrete
Concrete is the most widely used building material and a vital part of much of our modern infrastructure, from roads and dams to buildings and homes. Its hard-as-rock nature makes it ideal for housing and other large structures, but concrete’s ubiquity comes at a steep cost to the earth: it generates 8% of global carbon dioxide emissions and uses 2-3% of the world’s energy supply.
The high-temperature chemical process of making cement is responsible for concrete’s disproportionately huge carbon footprint. The good news is that the industry is working hard to reduce emissions and make concrete more climate-friendly.
For example, researchers are experimenting with using waste products to create cement, like slag from industrial processes and fly ash from coal-fired power plants. By incorporating these materials, it is possible to reduce the concrete’s carbon footprint without compromising its structural integrity.
Another way to cut a building’s embodied carbon is by limiting its construction, and reducing the amount of new materials used. This can be done by salvaging and reusing existing buildings, or by purchasing prefabricated building components.
By incorporating Tally into the design process, teams can calculate the embodied carbon of their project, and compare it to a baseline building. Tally also provides tools to find lower-carbon building materials, and links to the Inventory of Carbon & Energy database. The ICE database is free to download by clicking here.
Steel
A lot of attention goes to the operational carbon emissions a building generates when it’s in use, but what about the embodied carbon? The energy and carbon required to extract, refine, process, transport and fabricate construction materials also counts towards a building’s overall carbon footprint. This is called the embodied carbon life cycle and it’s an important factor to consider when choosing what goes into your next project.
Steel is a very durable material, easy to work with and has an excellent strength-to-weight ratio. It is a popular choice for residential and commercial projects, especially in areas where seismic issues are a concern. Steel has a high embodied carbon count, however, as it requires a large amount of energy to manufacture. The good news is that it can be recycled and there are several ways to minimize the impact on the environment by using recycled steel in your construction.
Wood has a much lower carbon footprint than concrete and steel. The main reason for this is that it is a renewable resource. Wood can be harvested and replanted over time, whereas iron or steel is a finite material that will eventually run out. Many of the newer engineered wood products used in construction are produced from sustainably harvested forests and have a low embodied carbon. Another great option is rammed earth, which uses only natural, locally sourced raw materials and can be built quickly and efficiently.
Glass
Glass is a common building material that can be found in every single home or office. It’s very easy to use and is known for its versatility, as it can be molded into different types of glass that have various functions. Glass is also a very durable material, able to resist changes in temperature and other environmental conditions.
However, glass is not as environmentally friendly as it is often believed. It’s actually one of the second most unsustainable building materials, with an average embodied carbon footprint of 3600kg CO2 per m3. This is partly due to its massive weight that requires significant amounts of energy for transportation.
In the production of glass, a lot of carbon emissions come from natural gas combustion in furnaces to heat limestone, sand and soda ash. This can be significantly reduced if recycled glass cullet is used instead, which requires no heating in the furnace and has a lower carbon footprint.
As architects and glaziers work to design more sustainable buildings, they must balance the reduction of emissions caused by a building’s operations with those produced during construction. This means looking at the whole life cycle of a building’s materials, including its embodied carbon. To do this, they can use the Inventory of Carbon and Energy (ICE) database from Bath University, which can be downloaded for free here.
Wood
Wood is a versatile building material that offers many benefits. Its low thermal conductivity makes it a good choice for energy-efficient designs, and its acoustic properties reduce echo and noise levels. It also has a natural tendency to absorb sound rather than reflect it, making it a suitable alternative to steel and concrete for multi-storey buildings. And it has a relatively low embodied carbon, especially when sourced from sustainably managed forests.
However, the impact of harvesting wood for use in construction is not carbon-neutral, and the losses of carbon stored by trees when they are used for fuel or burned in buildings should be accounted for. Ideally, this accounting will take into account the forest type (e.g., fast-growing pine versus slow-growing hardwood) and the time it takes for an ecosystem to reabsorb the carbon.
Nonetheless, the lack of clarity on biogenic carbon accounting can lead to skewed embodied carbon estimates for wooden buildings in LCAs. As a result, it is important that both the methodology and the quality of data in LCAs are considered when comparing the sustainability of building materials. Whether this information is provided as stand-alone reports, as verified datasets in large harmonized databases such as Gabi and SimaPro, or as Environmental Product Declarations (EPDs), the accuracy of these figures should be assessed.